Synthesizing hydrogen peroxide directly from hydrogen and oxygen would lower the cost of H2O2 production, making the oxidizing reagent an environmentally friendly substitute for chlorinated oxidizers in organic chemistry, wastewater treatment, and other processes. Direct synthesis involving metal catalysts generates significant amounts of water, which would necessitate costly separation and concentration steps. Instead, H2O2 is typically made from anthraquinones via a multistep process. But the catalytic inefficiencies could be overcome if the reaction mechanism were understood in fine detail, according to chemical engineers Neil M. Wilson and David W. Flaherty of the University of Illinois, Urbana-Champaign. To probe the mechanism, the team used nanosized palladium catalysts to investigate H2O2 synthesis over a range of hydrogen and oxygen pressures and solvent pH values. Their findings indicate that, in contrast to the commonly accepted mechanism, the reaction proceeds as follows: O2 adsorbs on the catalyst, draws two electrons from the catalyst, and reacts with two hydrogen ions from solution to form H2O2. Elsewhere on the catalyst surface, H2 adsorbs and dissociates, supplying the needed electrons and hydrogen ions (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b10669).